1. Field of the Invention
The present invention relates to a cable-driving apparatus used in the parking brake of a vehicle, and more particularly to a cable-driving apparatus which performs the function of an equalizer using a planet gear assembly, and a parking brake system using the cable-driving apparatus:
2. Description of the Prior Art
Generally, modern automobiles and other motor vehicles are provided with a power-assisted parking brake. The power-assisted parking brake is system that is electrically driven to remotely actuate the brake of a vehicle (generally, one of a front wheel brake and a rear wheel brake), thereby preventing the vehicle from being moved when it is parked. The system includes an electric motor and a rotational-to-linear driving mechanism, so that the rotational motion and torque of the motor can be converted into the linear displacement of the brake cable mechanically connected to the brake. When actuating the brake, as the motor is actuated, the brake cable is displaced, and braking is effected. Through a similar course, the braked state can be remotely released by reversely rotating the motor. In the event that a power supply system to the vehicle does not work (for example, in the case of towing), the braked state can be manually released using an emergency release mechanism, and the vehicle can be moved.
FIG. 1 illustrates the electronic parking brake 10 using a conventional cable-driving apparatus disclosed in Japanese Unexamined Patent Publication No. 2004-263812.
The electronic parking brake 10 includes rear cables 12 which are connected to the brake levers of wheels 11, an equalizer 13 which is connected to ends of the rear cables 12, and a front cable 14 which is connected to the equalizer 13. As the rear cables 12 and the front cable 14, a pull control cable is employed, in which a cable can freely slide in a tubular element. In the electronic parking brake 10, the front cable 14 is wound on a drum 15.
In the electronic parking brake 10, as a switch (not shown) is manipulated, braking can be effected or a braked state can be released through winding or unwinding of the front cable 14. That is to say, by rotating the motor provided in a cable-driving apparatus 17 and winding the front cable 14 on the drum 15, the front cable 14 and the rear cables 12 can be pulled against the resistant force of the return springs provided to the brake levers, and braking is effected. If the motor is rotated in a reverse direction, the drum 15 is reversely rotated, and the front cable 14 is unwound from the drum 15 by the elastic force of the return springs provided to the brake levers, and the braked state is released. The operation of the motor can be controlled by a controller 18. If an emergency situation such as the breakdown of an electrical system or a voltage drop occurs, by manipulating a release lever 16, a gear locking mechanism can be unlocked, and as a result, the parking brake system itself can be released.
In the conventional cable-driving apparatus and the electronic parking brake, as a driver manipulates a parking brake button, the motor is actuated, the rpm of the motor is reduced in a reduction gear box, and torque is increased. Consequently, as the cable is pulled, the parking brake operates. The conventional electronic parking brake encounters a problem in that, since a separate device is needed to realize the functionality of the equalizer, a structure is complicated, the size of a product increases, and production cost is increased.
Moreover, because the two rear cables are pulled by one driving motor, it is difficult to precisely equalize the tension applied to the two rear cables. Due to this fact, as a deviation is induced in the braking force applied to the respective wheels, braking efficiency deteriorates, and the passenger safety decreases.